A light emitting element driving device is known in which a plurality of light emitting element arrays respectively configured by a plurality of LEDs connected in series are connected in parallel and the plurality of light emitting element arrays are driven by constant current drivers respectively connected in series with each of the light emitting element arrays (for example, see JP-A-2003-332624). In this light emitting element driving device, the lowest voltage of the voltage applied to a plurality of constant current drivers is selected as a detection voltage, and then an output voltage of a power supply device is automatically controlled so that the value of the detected voltage is a reference voltage.